Amendment of Tax Return: How to Correct Your Self Assessment
Made a mistake on a tax return you've already submitted? You can normally correct it within 12 months of the statutory Self Assessment filing deadline. Even if that window has closed, there may still be a way to put matters right.
Can you amend a tax return after submitting it? Yes. HMRC normally allows you to amend a UK Self Assessment tax return within 12 months of the statutory filing deadline. You can correct missing income, expenses, tax reliefs and other mistakes. The change may increase your tax bill or produce a repayment.
Interactive Self Assessment amendment deadline checker
Choose the tax year of the return you want to correct. This shows the usual deadlines for returns with the standard 31 January statutory filing date.
Important: A late-issued notice to file can change the statutory filing and amendment dates. Enquiries, claims, elections and special circumstances may require different procedures. This tool does not assess eligibility for overpayment relief.
How to amend a Self Assessment tax return online
- Wait at least 72 hours after filing the original return.
- Sign in to your HMRC online account and open your Self Assessment account.
- Select More Self Assessment details, then At a glance and Tax return options.
- Choose the tax year you need to change.
- Correct the figures, check the tax calculation and submit the amended return again.
- Save the amended submission confirmation and review your updated Self Assessment statement.
If you used commercial tax software, amendments may need to be made using that software. Contact the provider if the amendment option is unavailable.
Self Assessment amendment deadlines
| Tax year | Normal amendment deadline | Normal overpayment relief deadline |
|---|---|---|
| 2025/26 | 31 January 2028 | 5 April 2030 |
| 2024/25 | 31 January 2027 | 5 April 2029 |
| 2023/24 | 31 January 2026 | 5 April 2028 |
| 2022/23 | 31 January 2025 | 5 April 2027 |
| 2021/22 | 31 January 2024 | 5 April 2026 |
The dates above assume standard Self Assessment filing dates. Overpayment relief is a separate statutory claim, not an extension of the online amendment facility.
What mistakes can you correct?
Check all affected return pages, not only the field where you first noticed the error. A correction can also change student loan repayments, the High Income Child Benefit Charge or payments on account.
What if the tax return amendment deadline has passed?
You owe additional tax
Write to HMRC explaining the relevant tax year, the omission or error, why it happened and the estimated additional tax. Sign the correspondence and retain supporting calculations. Interest may be due from the original payment deadline and penalties depend on the circumstances, including whether the error was careless or deliberate.
You paid too much tax
Consider whether you qualify for overpayment relief. A valid written claim generally needs to identify the tax year, explain the mistake and overpayment amount, address any earlier appeal and include the required signed declaration. Claims are subject to statutory restrictions; not every missed claim or relief can be recovered through this procedure. Your accountant can prepare the calculation, but the claimant must sign the declaration.
How do you amend a paper tax return?
Send corrected SA100 or relevant supplementary pages to HMRC. Mark each corrected page “amendment” and include your name and Unique Taxpayer Reference (UTR). Use the address on your Self Assessment paperwork, or HMRC's published Self Assessment postal address where appropriate. Keep copies and proof of posting.
What happens to your tax bill after an amendment?
An online amendment generally produces an updated calculation immediately; HMRC says the Self Assessment statement normally reflects the difference and any interest within three days. If the amendment increases the liability, check when payment is due. If it reduces liability, a refund may be available, but HMRC can make checks or offset other tax debts.
Example: a forgotten business expense
You filed a return reporting £42,000 of self-employment profit but later find £2,000 of allowable business expenses that were omitted. If the costs are deductible, the corrected profit would be £40,000. The actual tax saving depends on your other income, tax bands, National Insurance and any related calculations. Do not assume the saving is a fixed percentage of the expense.
Before you submit an amended return
- Reconcile the original return with your accounts, bank records and tax certificates.
- Check whether the correction affects more than one tax year.
- Review any consequential adjustments to payments on account.
- Confirm whether a separate capital gains or other reporting obligation applies.
- Keep evidence and a clear record of why the return was changed.
Frequently asked questions
Can I amend my tax return after 31 January?
Yes. For a return with the normal filing deadline, you usually have a further 12 months after 31 January to amend it. For example, the usual deadline to amend a 2024/25 return is 31 January 2027.
Can I amend a tax return from three years ago?
Usually not through the standard online amendment process. Depending on the tax year and the type of error, you may need to write to HMRC or consider an eligible overpayment relief claim.
Will I be fined for correcting my tax return?
Not automatically. A genuine mistake does not by itself trigger a penalty. HMRC considers whether reasonable care was taken and the nature of any inaccuracy. Additional tax can attract interest.
How long does HMRC take to update an amended return?
Online calculations generally update immediately and HMRC says statement adjustments normally appear within three days. Paper amendments, repayments and cases requiring review can take longer.
Can an accountant amend my Self Assessment return?
Yes, an authorised tax agent can normally submit amendments on your behalf. Some statutory claims, including overpayment relief, require your own signed declaration.
Can I change a company Corporation Tax return in the same way?
No. A company's CT600 is subject to a different Corporation Tax amendment process and deadline. See our CT600 guide.
Related guidance
Read our guides to filing a Self Assessment tax return, Self Assessment deadlines, finding your UTR and HMRC Time to Pay.
Need help correcting a tax return?
The Online Accountants supports UK taxpayers with Self Assessment preparation, review and amendments. We can help identify the correct procedure, calculate the revised liability and explain the next steps. Fees for amendment work depend on the circumstances and will be confirmed before work begins.
Explore our Self Assessment serviceReviewed for general UK Self Assessment guidance in October 2026. This page does not replace tailored advice. Rules and deadlines can vary where HMRC issued a late notice to file or an enquiry is in progress.